This invention relates to carrier subscriber telephone station terminal equipment, and more particularly to electrical circuitry in a carrier subscriber station which may make the available current in the loop there be greater than that provided by only a local battery there.
Carrier subscriber telephone station terminal equipment is available which is designed to operate from a 6 volt local battery that is charged by line current from a central office battery. This means that the available local supply voltage in a station terminal for operating a handset and electrical circuits in the subscriber station terminal is less than 6 volts by an amount which depends on the level of charge on the local battery. This battery voltage provides adequate loop current for operating conventional rotary dial telephone sets. It has been found, however, that such a local battery voltage does not provide sufficient current in the station terminal loop for operating some Touch-Tone type telephone sets. More specifically, it does not provide adequate current for operating on high resistance loops such as are experienced with button-down operation of touch calling telephone sets equipped with polarity guard bridge rectifiers.
An object of this invention is the provision of a circuit which may cause the available supply voltage at a subscriber station to be greater than the local battery voltage there for increasing the current supplied in a station terminal loop supplied to the subscriber telephone set.